CH628256A5 - METHOD AND DEVICE FOR THE FINE SIZING OF MATERIALS IN INELASTIC STATE. - Google Patents

Description

The invention relates to a method and an apparatus for the fine comminution of inelastic materials and of materials which are brought into an inelastic state by supplying heat and / or by supplying and converting mechanical energy into heat. 25 regrind particles of many finely shredded materials deform practically inelastically when subjected to large loads, such as those that occur in particular under pressure, shear or impact loads in shredding machines. That applies to

30 - materials that have a low yield point even at normal temperature, e.g. many polymers and in particular the thermoplastic polymers (poly-tetrafluoroethylene, polyethylene, polypropylene, polyamide etc.), organic chemicals and plastic metals 35 (e.g. copper),

- Materials that are mostly elastic at normal temperature and low loads, but heat up due to the load and react more inelastically, e.g. Polystyrene, polyme-40 methyl methacrylate,

- Materials that can be plasticized under high pressures, e.g. Alkali halides.

Inelastic materials are considered to be those in whose force-deformation diagram of a loading and unloading process 45 the loading and unloading curves do not coincide. The former is flatter than the relief curve. The area circumscribed by both curves is a measure of the inelastic deformation. In contrast, there are covering load and relief curves for elastic materials. Two forms of inelasticity can be distinguished: viscous flow and plastic deformation. Which of the two mainly determines the material behavior depends on the molecular structure of the substance and, for a given substance, on temperature, speed 55 and intensity of the stress. The inelastic behavior increases with increasing temperature or with decreasing loading speed.

There is a general tendency that, as the grain size decreases, the ability of regrind particles to show inelastic behavior, i.e. to deform inelastically, is increased. This applies in particular to particle sizes below 1 mm. For the fine comminution, regrind particles also behave practically inelastic, even those materials that are usually considered to be elastic or only slightly inelastic. -

An inelastic material behavior considerably complicates the shredding of many substances, especially tough substances. Therefore, many materials of the above can be used

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It is difficult to grind groups in the grain size range below 1 mm.

The prior art shows the following ways to overcome these difficulties:

- Reduction of inelasticity due to stress with high deformation rates and / or cooling in order to promote the development of brittle fractures (embrittlement of the particles), i.e. to cause the predominantly elastic deformation of the body until it breaks,

- A pronounced shear stress, as can be realized on edges and cutting edges (cutting the particles).

High deformation speeds are achieved in impact mills of all kinds and in air jet mills. These mills can be operated with a large air or gas throughput, which facilitates the cooling of the ground material. Impact mills are therefore particularly suitable for the fine grinding of inelastic materials. In the case of very pronounced inelastic behavior, the embrittlement by cooling with liquid gas, e.g. liquid nitrogen. The crushing takes place in cold grinding plants, which can be equipped with mills of all kinds, e.g. Impact mills, disc mills, vibratory mills and the like

A pronounced shear stress on edges and cutting edges is achieved with granulators, granulators, disc mills and also with impact mills with profiled grinding tools. Cutting mills and cutting granulators are particularly suitable for the production of particles whose size is over one millimeter. Disc. Mills and impact mills with profiled grinding tools are used for grinding down to grain sizes of 200 (in.

The energy requirement for fine grinding of inelastic materials or for the comminution of inelastic materials is considerable and, depending on the material and fineness, is between 50 and 1500 kWh / t. The throughput rates decrease significantly for a given mill if larger finenesses are to be produced, e.g. for plastics by 80% if the maximum grain size of the finished product is to be reduced from 800 µm to 200 µm. In the case of very inelastic materials, this fineness can often only be achieved with throughputs between 10 and 40 kg / h with mills of conventional size.

Of particularly pronounced inelastic materials, e.g. Polyethylene, polytetrafluoroethylene, polypropylene and copper, particles under 50 [im almost not by grinding; Powder of this fineness is obtained by precipitation from solutions or spraying from melts.

The invention has for its object to provide a method and a device for the fine grinding of inelastic materials, i.e. for crushing to average volume-related particle sizes of about 10 μm to 2 mm, in particular 10 to 500 μm, with which in particular the materials mentioned are less difficult and require less mechanical effort, as well as energy requirements and / or with the same energy requirements, to greater finenesses can be shredded as before without the need for expensive cold grinding.

The solution to this problem is based on a method for comminuting inelastic materials of the groups of substances mentioned at the outset and is characterized according to claim 1 in that the material to be comminuted is first pushed into recesses or cavities by a compressive load, the dimensions of which are matched to the fineness to be achieved , and that after this process the material residues that still connect the partial particles are destroyed by relative movements of the partial particles and the partial particles are removed from recesses or cavities and a press for carrying out the method, which is characterized in that at least in one of the work surfaces recesses are provided in the press, the size of which corresponds to that of the partial particles to be achieved.

The method according to the invention is characterized by advantageous configurations in the dependent claims and comprises the following essential method steps:

1. The material to be shredded, which can be in the form of small particles, threads, plates or foils,

If it is not sufficiently inelastic by nature, it is tempered in such a way that it becomes sufficiently inelastic, in particular flowable, in the event of a subsequent pressure load in order to be able to be pushed into small cavities or recesses. This tempering can take place before the stressing process or during this by adding heat and / or the mechanical work being carried out.

2. The originally inelastic or the tempered material, which now behaves inelastically, is forced into small recesses or cavities in accordance with the fineness to be achieved by mechanically induced pressure. The recesses or cavities can either be formed in the upper or working surface of grinding tools or can be formed by a bed of loose, appropriately shaped and dimensioned grinding bodies.

As a result of the mechanically induced pressure, the material is pressed into the recesses or cavities, so that partial particles of the desired size or size distribution are produced. These partial particles are almost always connected by lamellar or web-like material residues.

3. During process step 2 or thereafter, the lamellar or web-like connections between the partial particles are destroyed by a relative movement of the partial particles with respect to one another, thereby isolating them from one another.

4. Particles and grinding tools or grinding media are separated from one another, optionally after an upstream disintegration step.

By using grinding tools with recesses that have a size distribution similar to the grain size distribution to be achieved, or by using a bed of grinding media with a certain grain size distribution, so that the open spaces between grinding media that are open to the outside are similar to the grain size distribution to be achieved Void volume distribution can be obtained not only monodisperse powders but also those that have a predetermined particle size distribution.

Known presses, such as roller presses, screw presses, punch presses or the like, are fundamentally suitable for carrying out the method according to the invention, although these are expediently to be adapted to the special requirements of the proposed fine comminution.

In the case of a roller press for carrying out the method, it is provided that at least one of the rollers has recesses in the working surface, the size of which corresponds or is similar to the size distribution of the partial particles to be achieved. The recesses can be formed in that grooves and cams are provided in the working surfaces of the rollers and the cams of one roller engage in the grooves of the other roller. As a result, small cutouts are made in the circumferential and axial directions, similar to gears

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trained in the area of the nip. The recesses per se and in particular those between the cams and webs are preferably flared outwards in order to facilitate the ejection of the partial particles.

To pressurize mixtures of grinding media and regrind, roller presses can also be used which have smooth rollers, or those in the manner of briquette presses in which at least one roller has recesses in the working surface, the size of which to form compacts is several times that of the together with the grinding media to be crushed material. This creates briquette-like compacts from grinding media and regrind. In order to effect the separation of the partial particles formed, it is optionally provided to drive the rollers at different speeds. In this way, comparatively small particles can be obtained even with comparatively large cutouts.

Naturally, the pure regrind particles in particular tend to adhere to the roller surface and in particular in the recesses formed. An embodiment of the roller press therefore provides that, in addition to the rollers, a device is provided for ejecting the material that has penetrated into the recesses. Such ejection devices can be designed as a brush, as gears engaging in the recesses with a straight or inclined tooth surface, or in the form of jet nozzles for compressed gas or pressure liquid directed onto the recesses. There are also other configurations of ejection devices, as are known in press granulators and briquetting rolls.

In order to make it easy for granular ground material to be drawn into the nip, it is advisable to provide a sufficiently high chute above the nip. For comminution with the aid of grinding media, it can then be expedient to provide a double chute consisting of an inner chute for the ground material and an outer chute for the grinding media.

In addition to roller presses, screw presses are also suitable for continuous fine grinding. The screw spindle can be cylindrical or, in particular, conical. In such a screw press, the counter bearing to the press screw, that is to say the bearing against which the screw conveys the feed material, can be resiliently supported, for example by springs or by a hydropneumatic cylinder. This allows a certain maximum pressure to be maintained in the compression chamber. Pellets are formed which are destroyed by intermeshing pin or cam rings in the outlet gap which are driven in opposite directions. Depending on the speed difference, the compact can be more or less dissolved into the individual regrind particles and grinding media.

The fine comminution of smaller batches can also be carried out in a stamping press with a press piston and a counter-piston, the latter being withdrawn from the press chamber after a completed press stroke, so that the formed compact can be ejected by further advancing the press piston. This stamp press is suitable for the pressure loading of a mixture of grinding media and regrind. An embodiment of such a stamp press known per se for the particularly advantageous implementation of the method according to the invention provides that at least the counter-piston can be rotated and is provided with shear pins projecting into the press chamber. As a result, extensive disintegration of the compact formed in the press space can be achieved, so that the subsequent separation of the grinding media from the particles formed and the destruction of the webs connecting these particles to one another can already be started in the press space.

The invention is explained in more detail with advantageous details using exemplary embodiments with reference to a drawing, in which:

1 is a schematic diagram of various stages of comminution of an individual regrind,

2 three working positions of a stamp press for comminuting regrind particles in a collective with grinding media,

3 shows a stamp press with shear pins on the press stamp and on the counter stamp in a partial and complete closed position,

Fig. 4 is a roller press with profiled rollers for performing the method according to the invention, namely Fig. 4a is a sectional view, Fig. 4b is an end view of the press roller on an enlarged scale with a device for ejecting the partial particles, Fig. 4c is a plan view of the Pair of press rolls, FIG. 4d an ejection device in the form of jet nozzles assigned to a press roll, FIG. 4e a partial section of the intermeshing press rolls in the area of the roll gap in the axis-normal and axially parallel section, FIG Roll nip, these having conical cams, in the axis-normal and axially parallel section, Fig. 4g a pair of rollers in the area of the nip with interlocking webs that have axially parallel bores.

5 shows a roller press with smooth rollers for processing mixtures of regrind particles and grinding media and

Fig. 6 is a screw press in longitudinal section.

Fig. 1 shows an embodiment of the inventive idea with grinding tools in the form of plates 1 and 1 'with groove-shaped recesses and standing webs in various successive relative positions [(a.) 1st opening position, (b.) 1st closing position, (e. ) 2nd closing position (after relative displacement of the plates), (d.) 2nd opening position (before ejection of the partial particles) and (e.) 3rd opening position (after ejection of the partial particles)] in two orthogonal views. Both plates 1 and 1 'are mutually movable and parallel to each other. A regrind particle 2 is detected during the closing stroke, pressed and pushed into several recesses. The resulting partial particles 3 in the recesses are almost always connected by lamellar material residues 4, the thickness of which is determined by the design. These slats or material residues are destroyed by a relative movement in the tangential direction. During the opening stroke or thereafter, an ejection device 5 ejects the now separated partial particles 3 from the recesses. The groove-like profiling of the working surfaces of the grinding tools creates elongated partial particles. The elongated partial particles can be converted into cubic particles by repeated application with a preferred orientation transverse to the cutouts.

Fig. 2 is used to explain the realization of the inventive concept with grinding balls of approximately the same size as grinding tools. A mixture of regrind particles 2 and grinding balls 6 is initially loosely in a press chamber 8 (Fig. 2a). The balls are smaller than the particles in order to obtain a usable degree of comminution; the size ratio can be between 1: 3 and 1:20 and depends on the required degree of comminution and the deformation resistance of the particles, which determines the pressure to be applied for a given size of the grinding balls. The mixing ratio of material to be crushed (regrind) to grinding balls is adjusted so that the regrind volume roughly corresponds to the cavity volume of the ball

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fill corresponds. From an operational point of view, it may be more economical to work with excess material so that grinding ball bridges do not occur between pistons and abutments in some areas. The mixture is then compressed against a counter-piston 10 by means of a press piston 9 until the balls are packed as densely as possible (FIG. 2b and detail “A”). The ground material is forced into the cavities between the balls by the compression. This creates partial particles 3, which are still connected by web-like material residues 7. This compression process produces a type of compact 12, the cohesion of which is essentially determined by the cohesion in the ground material, but also by the adhesive forces between the ground material and the ground ball. In extreme cases, a compact pellet 12 can be formed with the regrind as a connecting matrix and the grinding balls as deposits. After compression, the compact 12 is ejected by moving the plunger 9 forward and retracting the counter-piston 10 (FIG. 2c). The compact 12 is then destroyed by impact or friction; the web-like material remnants 7 tear between the partial particles 3. In a subsequent separation process, the grinding balls are separated from the ground material. The separation can be carried out according to one of the known separation processes.

The densest ball packing made of balls of the same size has cavities of two different sizes, namely approx. 22% and approx. 42% of the ball diameter. With a fraction of balls of somewhat different sizes and with a packing that is not completely regular, voids of up to approx. 50% of the ball diameter arise. For the degree of comminution z this results if the ratio of the maximum feed particle size xniax to the maximum partial particle size dmax = 0.5 d is defined, z = 2xmax / d. In order to produce a grinding product with a grain size of less than 50 µm, grinding balls with a diameter of 100 µm are to be used.

FIG. 3 shows in a largely open (FIG. 3 a) and a largely closed position (FIG. 3 b) a modified press device, the press piston 9 and counter piston 10 of which are rotatable and each have shear pins 14. A slow rotation of the plunger prevents the formation of bridges between the pins between the plunger and counter-piston and causes the material residues and connections between the partial particles 3 to be destroyed during the compression process.

Three exemplary embodiments of a device for carrying out the method according to the invention are described below.

4a to 4g show a roller press with two parallel profiled working surfaces 16 which are formed by press rollers, the peripheral speeds of which can be set differently. The regrind particles are optionally preheated in a preheater until inelastic behavior and fall through a funnel-shaped feed shaft 15 into the nip. Each roller has circumferential grooves 17 (Figs. 4b to 4e) of depth t 'and width b' (Fig. 4e). Crosspieces 18 between the grooves 17 have the width b and are provided with conical milled recesses 19 of the width w and the depth t. These recesses 19 do not extend to the bottom of the circumferential grooves 17, so that t is smaller than t '. Cams 20 of length 1, width b and height t remain between the recesses 19. Both press rollers 16 are adjusted so that the webs 18 of one run in the grooves 17 of the other roller and immerse the webs so deep that their upper edge runs below the recess base. The regrind in the form of particles 2 or foils is pressed into several recesses 19 of both press rolls 16 during the drawing-in; there are partial particles 3 that completely or partially fill the grooves. As a result of the differential movement between the press rolls 16, the connecting lamellae between the partial particles are destroyed. To ensure this, the difference between the overlap must be at least size (w + 1). Gears 21 or co-rotating brushes 22 or plungers are used as ejection devices, as are common on gear granulators or briquetting roller presses. The ejection can also be done by compressed air or pressure fluid that flows out from laterally arranged nozzles 23 (FIG. 4d). For some materials it is sufficient to wipe the grooves with a wetting liquid, e.g. Spray water or methanol so that the centrifugal force alone is sufficient to eject the partial particles. This method is favored by a conical shape of the grooves. The width and depth of the recesses 19 can be the same size as the width b of the webs 18, ie w = t = b; different dimensions are also possible, ie w ^ b, t ^ b and w ^ t; other forms of recesses are also possible. A roller can have grooves and recesses of different dimensions, e.g. bj <b2 <b3 etc. as well as tj <t2 <t3 etc. and have different shapes, so that a particle collective with particles of different sizes and shapes is created,

if such a product specification is required.

Another form of profiling is shown in FIG. 4f. Grooves and ridges are radially conical. If the flanks of the cams are also conical, the recesses are given a shape which favors the ejection of the partial particles. The press roller apparatus can also be operated in such a way that the sub-particles are pushed out laterally by newly fed regrind particles during subsequent rotations. Since both rollers rotate at different circumferential speeds, the cams of the other roller cut the part particles that slide out into parts; there is a collective of particles of different sizes down to a tenth or twentieth the size of the recesses. In this mode of operation, press rolls can also be used, the webs 18 of which have axially parallel bores 24 between the grooves (FIG. 4g).

Cam rollers can be loaded with particles whose linear dimensions are up to ten times larger than the dimensions of the cutouts. For design reasons, the lower limit of millings is approximately 0.3 mm X 0.3 mm. The lower limit for holes can be 0.1 mm.

5a shows a roller press in which a mixture of regrind 2 and grinding balls 6 is pressed between two rotating smooth press rollers 28. The mixture, which may need to be preheated in a preheater to a temperature which ensures a predominantly inelastic behavior of the millbase, is fed into the roll gap 34 from above via a drop shaft 29 of a corresponding height and enters at a speed which corresponds approximately to the roll circumferential speed. A roller is arranged to be movable and is pressed against a stop 31 by means of prestressed springs 30 or hydraulically. Grist and grinding balls can either be added as a mixture (Fig. 5a) or in layers (Fig. 5b) by feeding the grist particles 2 through an inner chute 32 and the grit balls 6 through an outer chute 33, so that on both sides of the Grind the grinding balls towards the nip. In the case of regrind particles shaped like foils or plates, this subdivided type of task is also useful. The mixture is compacted in the roller gap 34 and the ground material is forced into the cavities between the grinding balls 6. Flat-shaped compacts 35 are formed which

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must finally be destroyed. The regrind and balls are separated from each other by sieving, air separation or magnetic separation. A combination of the separation methods can also be used.

The size of the cavities between the grinding balls depends on their size and shape. A desired particle size distribution of the grinding product can be adjusted by varying the size composition of the grinding balls. With spheres of 100 [in diameter, collectives between 10 (im and 60 [im.

Instead of grinding balls, cylinder sections or irregularly shaped grinding media can also be used.

A mixture of regrind particles 2 and grinding media 6 can also be compressed in a screw press, as shown in FIG. 6. A press screw (screw spindle) 38 conveys the mixture against a resilient counter bearing 39, which is pressed upwards in the axial direction by means of springs 40. This allows a fixed, predetermined maximum pressure to be set in the press room. The counter bearing 39 deviates downwards in accordance with the delivery capacity of the screw and the set pressure, so that the ground material / grinding media mixture can exit radially through an outlet gap 37. The shaft 41 of the press screw 38 is equipped in the press space between the latter and the outlet gap 37 with a shear pin 42 which also rotates. Bridges formed from grinding media 6 and regrind are destroyed and the mixture is subjected to a relative movement which supports the separation of the partial particles from one another. The counter bearing 39 also rotates and has a ring of shear pins 44 further out in the horizontal outlet gap 37, in the vicinity of which another shear pin ring 43 is attached to the housing 45 of the 5 screw press with which the ring 44 meshes. These shear pins have the task of closing the press cake destroy so that the subsequent separation of the grinding stock and grinding media is possible. Depending on requirements, the screw press can also be equipped with more than two '10 shear pin rings. The worm housing 45 and the counter bearing 39 optionally have channels 46 for cooling or heating liquids in order to keep the temperature in the pressing chamber at the optimum point in terms of process technology. .

15 In addition to the described three exemplary embodiments of a press for carrying out the method according to the invention, others can also be developed by means of which the new comminution method can be carried out, which has lower values in terms of throughput and labor requirements than the previous methods.

For example, for the comminution of high-pressure polyethylene granules to a product with a particle size of 100% <250 [im, 50% <150 [im and 30%. <100 [im a work requirement of approx. 50 to 80 kWh / t not-25 maneuverable. Devices according to the invention of the size of the impact mills normally used achieve throughputs of up to 200 kg / h. In the case of impact grinding, on the other hand, the work requirement is over 500 kWh / t, the throughputs are less than 50 kg / h.

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Claims (15)

628256 1. A method for the fine comminution of inelastic materials and of materials which are brought into a state of inelastic behavior by heat and / or by supplying and converting mechanical energy into heat, characterized in that the material to be comminuted is initially subjected to a pressure load in recesses or cavities is pushed, the dimensions of which are matched to the fineness to be achieved, and that after this process the material residues which still connect the partial particles are destroyed by relative movements of the partial particles and the partial particles are removed from the recesses or cavities. 2. The method according to claim 1, characterized in that the material to be shredded is pushed into recesses which are formed in the working surfaces of the grinding tools which apply the pressure, 2nd PATENT CLAIMS 3. The method according to claim 2, characterized in that the material to be shredded is pushed into recesses of different sizes and / or shapes, the size and / or shape distribution of which corresponds to the size and / or shape distribution of the partial particles to be obtained. 4. The method according to claim 1, characterized in that the material to be comminuted in cavities of a bed of grinding media of greater strength than the material to be comminuted, in particular after prior mixing with the grinding media, pressed and separated from the cavities after removal from the cavities. 5 records that the ejector in the recesses (19) engaging gears (21) with straight or inclined tooth surfaces. 16. Roller press according to claim 13, characterized in that the ejection device in the recesses 5. The method according to claim 4, characterized in that the material to be comminuted and the grinding media are arranged in layers before the compressive stress. 6. The method according to any one of claims 4 or 5, characterized in that the material to be crushed is forced into the cavities of a bed of grinding media of different sizes, which form a void volume distribution that corresponds to the particle size distribution to be achieved. 7. The method according to any one of claims 4 to 6, characterized in that the material residues connecting the regrind particles are destroyed by an impact load or by a pressure-shear stress of the mixture in the form of a compact from grinding media and regrind. 8. roller press for carrying out the method according to claim 2, characterized in that recesses (19) are provided in at least one of the working surfaces of the press roller, the size of which corresponds to that of the partial particles to be achieved. 9. Roll press according to claim 8, for carrying out the method according to claim 3, characterized in that the recesses (19) have a size distribution which corresponds to the size distribution of the partial particles to be achieved. 10 (19) directed jet nozzles (23) for compressed gas or liquid. 17. Roller press according to one of claims 8 to 16, characterized in that above a roller gap (34), a chute (29) for the ground material to be comminuted. 10. Roll press according to claim 8, characterized in that grooves (17) and cams (20) are provided in the working surfaces of the press rolls (16) and the cams of one roll engage in the grooves of the other roll. 11. Roll press according to claim 10, characterized in that the recesses (19) between the cams (20) and the grooves (17) are designed to widen conically outwards. 12. Roll press according to one of claims 8 to 11, characterized in that the press rolls (16) can be driven at different speeds. 13. Roll press according to one of claims 8 to 12, characterized in that in addition to the press rolls (16), a device for ejecting the material pushed into the recesses (19) is provided. 14. Roller press according to claim 13, characterized in that the ejection device on the rollers (16) engaging, rotating brushes (22). 15. Roll press according to claim 13, characterized 15 is seen.